Mother-to-child-transmission (MTCT) of HIV continues to be high in developing countries where breast-feeding is a necessary means to provide nutrients and protective immunity against many co- infecting pathogens to HIV-1 exposed infants. Thus, a pediatric HIV vaccine is urgently needed. Our goal is to identify adjuvants and vaccine delivery strategies that can prevent breast milk transmission of HIV in newborns. The immaturity of the infant immune system is a unique challenge in pediatric vaccine design. We rationalized that immune mediators aimed at increasing infant dendritic cell (DC) maturation would improve T cell and promote T helper 1 responses. In addition, adjuvants that can overcome the need for CD4 help would result in more efficient B cell stimulation. Specifically, the proposed grant application will test whether dendritic cell function and antibody quality can be improved by co-administration of GM-CSF (Aim 1) and CD40L (Aim 2) with the DNA prime. The GM-CSF adjuvant will recruit DC, enhance DC function, and has consistently been shown to increase antibody response in SIV vaccinated adult macaques. The CD40L adjuvant will provide needed co-stimulation for more efficient induction of B cell responses in infants. We further predict that such adjuvants would be most beneficial when the infant immune system is most immature, and would, thus, have to be provided during the prime phase of the vaccine regimen. Towards our long-term goal, the studies here will test GM-CSF and CD40L as adjuvants using a model intramuscular DNA/MVA vaccine that has demonstrated efficacy in the prevention against rectal SIV or SHIV transmission in adult macaques. We will first confirm that this adjuvanted DNA/ MVA vaccine can enhance protective efficacy against oral SIV acquisition in infants, and then demonstrate that oral vaccine delivery would be even more effective. We hypothesize that the oral application of these adjuvants with the DNA prime (Aim 3) will promote the induction of local immune responses, including IgA and HIV-specific T cells that would home to the oral mucosa. Immune responses generated at the site of viral entry should be most protective against oral HIV acquisition by breast milk. Thus, the main focus lies in the identification of immune adjuvants and delivery strategies that can enhance the protective efficacy of pediatric HIV vaccines. The studies will be performed in the infant rhesus macaque model of oral SIV infection. The results are expected to identify (i) adjuvants that can increase protective efficacy, and (ii) vaccine delivery strategies that enhance local immune responses to prevent oral HIV acquisition in infants. The combined expertise of (1) Dr. Abel in infant SIV pathogenesis and vaccine studies, (2) Dr. Kozlowski in mucosal immunology, and (3) the expertise of Dr. Amara in HIV vaccine design will guarantee the successful completion of the proposed studies. PUBLIC HEALTH RELEVANCE: The proposed studies address an important global health issue, the prevention of Mother-to-Child-Transmission (MTCT) of HIV-1 through breast milk transmission. One of the major challenges in developing a pediatric HIV vaccine is the immaturity of the infant's immune system. Therefore, in a proof-of-concept study, we propose to test whether immunomodulatory compounds administered during the vaccine prime will enhance infant dendritic cell activation and maturation and thereby improve vaccine- induced adaptive immune responses. We will perform these studies in the infant macaque model of oral SIV infection using a DNA/MVA prime-boost regimen that has demonstrated partial protective efficacy in infants and adults. Furthermore, we will determine whether oral application of the adjuvanted DNA prime the vaccine will result in better induction of vaccine-induced immune responses at the site of viral entry compared to systemic administration. A comprehensive analysis of local mucosal and systemic immune responses will be performed to evaluate immunogenicity and efficacy of this pediatric adjuvanted DNA/MVA SIV vaccine.